SLVSCK4A September   2015  – May 2016 TPS61235P , TPS61236P

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Boost Controller Operation
      2. 8.3.2  Soft Start
      3. 8.3.3  Enable and Disable
      4. 8.3.4  Constant Output Voltage and Constant Output Current Operations
        1. 8.3.4.1 Constant Voltage Operation
        2. 8.3.4.2 Output Current Monitor
        3. 8.3.4.3 Constant Current Operation
      5. 8.3.5  Over Current Protection
      6. 8.3.6  Load Status Indication
      7. 8.3.7  Under voltage Lockout
      8. 8.3.8  Over Voltage Protection and Reverse Current Block
      9. 8.3.9  Short Circuit Protection
      10. 8.3.10 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 PWM Mode
      2. 8.4.2 PFM Mode
      3. 8.4.3 CV Mode and CC Mode
  9. Applications and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 TPS61236P 3-V to 4.35-V Input, 5-V Output Voltage, 3-A Maximum Output Current
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Programming the Output Voltage
          2. 9.2.1.2.2 Program the Constant Output Current
          3. 9.2.1.2.3 Inductor and Capacitor Selection
            1. 9.2.1.2.3.1 Inductor Selection
            2. 9.2.1.2.3.2 Output Capacitor Selection
            3. 9.2.1.2.3.3 Input Capacitor Selection
          4. 9.2.1.2.4 Loop Stability, Feed Forward Capacitor
          5. 9.2.1.2.5 INACT Pin Pull-up Resistor
        3. 9.2.1.3 TPS61236P 5-V Output Application Curves
      2. 9.2.2 TPS61236P 2.3-V to 5-V Input, 5-V 2-A Output Converter
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 TPS61236P 5-V Output Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Related Links
    4. 12.4 Receiving Notification of Documentation Updates
    5. 12.5 Community Resources
    6. 12.6 Trademarks
    7. 12.7 Electrostatic Discharge Caution
    8. 12.8 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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9 Applications and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

The TPS6123x family is designed to operate from an input voltage supply range from 2.3-V to (VOUT – 0.6)-V, and the maximum output voltage can be up to 5.5-V. The device operates in PWM mode under medium to heavy load conditions and in power save mode under light load condition. In PWM mode, the TPS6123x converter operates with 1-MHz switching frequency which provides a controlled frequency variation over the input voltage range. As load current decreases, the converter enters PFM mode, reducing switching frequency and minimizing IC quiescent current to achieve high efficiency over the entire load current range. The TPS6123x also supports a constant current output feature to limit the maximum output current at a programmed value.

9.2 Typical Applications

9.2.1 TPS61236P 3-V to 4.35-V Input, 5-V Output Voltage, 3-A Maximum Output Current

This example illustrates how to use the TPS61236P to generate a 5-V output voltage from a Li-ion battery input and how to use the CC function to limit maximum output current to 3-A for the entire input voltage range.

TPS61235P TPS61236P TypApp_3.0A.gif Figure 16. TPS61236P 5-V Output with 3-A Constant Output Current

9.2.1.1 Design Requirements

The design parameters for the TPS61236P 5-V 3-A constant output current design are listed in Table 1.

Table 1. TPS61236P 5-V 3-A Constant Output Current Design Parameters

DESIGN PARAMETERS EXAMPLE VALUES
Input voltage range 3 V to 4.35 V
Output voltage 5 V
Output current limit 3 A
Operating frequency 1 MHz

9.2.1.2 Detailed Design Procedure

The following sections describe the selection process of the external components. The following table summaries the final component selections.

Table 2. List of Components for TPS61236P 5-V Output with 3-A Constant Output Current Application

REFERENCE DESCRIPTION MANUFACTURER(1)
L1 1.0 μH, Power Inductor, XAL7030 Coilcraft
C1 10 μF 6.3 V, 0603, X5R ceramic, GRM188R60J106ME84 Murata
C2 3 × 22 μF 10 V, 0805, X5R ceramic, GRM21BR61A226ME44 Murata
C3 10 nF, 50 V, 0603, X5R ceramic, GRM188R61H103KA01D Murata
C4 1 µF, 6.3 V, 0402, X5R ceramic, GRM152R60J105ME15 Murata
R1 1 MΩ, Resistor, Chip, 1/10W, 1% Rohm
R2 332 kΩ, Resistor, Chip, 1/10W, 0.5% Rohm
R3 41.2 kΩ, Resistor, Chip, 1/10W, 0.5% Rohm
R4 1 MΩ, Resistor, Chip, 1/10W, 1% Rohm
R5 1 MΩ, Resistor, Chip, 1/10W, 1% Rohm

9.2.1.2.1 Programming the Output Voltage

The TPS61236P's output voltage needs to be programmed via an external voltage divider at the FB pin, as shown in Figure 16.

By selecting R1 and R2, the output voltage is programmed to the desired value. When the output voltage is regulated, the typical voltage at the FB pin is VFB. The following equation can be used to calculate R1 and R2.

Equation 6. TPS61235P TPS61236P EQ_VOUT.gif

For the best accuracy, the current following through R2 should be 100 times larger than FB pin leakage current. Changing R2 towards a lower value increases the robustness against noise injection. Changing R2 towards higher values reduces the FB divider current for achieving the highest efficiency at low load currents.

For the fixed output voltage version, TPS61235P, the FB pin must be tied to the output directly.

In this example, 1-MΩ and 332-kΩ resistors are selected for R1 and R2. High accuracy like 0.5% resistors are recommended for better output voltage accuracy.

9.2.1.2.2 Program the Constant Output Current

The TPS6123x's constant output current can be programmed via an external resistor RCC at the CC pin.

Because the TPS6123x has an internal current limit function to protect the IC from over load situations, a user should make sure the constant output current is set within the device's maximum load capability. If the constant current is set too high, the output current will be limited by internal protection circuitry and cannot reach the set value.

The maximum output capability is determined by the input to output voltage ratio and the internal current limit ILIM. Refer to Equation 3, Equation 4, and Equation 5 for the maximum output current calculation. The minimum input voltage, minimum current limit value, and maximum switching frequency value shall be used for the worst case calculation.

In this example, the minimum input voltage is 3-V and output voltage is 5-V. The efficiency η can be estimated as 85% for the worst case condition. By checking the specification table, the minimum ILIM value is 6.5-A, and maximum switching frequency fSW is 1250-kHz, so the calculation result of the maximum output current under the worse case condition is 3.6-A.

After calculation, the 3-A constant current target is within the maximum output current range, so the user can set it. Equation 2 can be used to select RCC (R3 in Figure 16). In this example, the calculation result of R3 is 41.47-kΩ. A 1% accuracy 41.2-kΩ resistor is selected. By using it, the constant output current can be regulated at 3-A typically.

C3 must be connected in parallel with R3 to average the CC pin voltage and also stabilize the control loop. A larger capacitor can smooth the CC voltage better, and also slow down the loop response. Normally a 10-nF capacitor is recommended.

If the Constant Current function is not needed, the user can simply connect the CC pin to ground to disable it. Under this configuration, the TPS6123x works as a normal boost converter, and its maximum output current is decided by the internal current limit circuitry.

9.2.1.2.3 Inductor and Capacitor Selection

A boost converter requires two main passive components for storing energy during the conversion, an inductor and an output capacitor. Please refer to the following sections to select the inductor and capacitor. Also refer to the Recommended Operating Conditions for operation recommendations.

9.2.1.2.3.1 Inductor Selection

Because a 1-µH inductor normally has a higher current rating and smaller form factor than inductors of higher values, the TPS6123x is optimized for 1-µH inductor operation. Inductors of other values may cause control loop instability and so are not recommended.

It is advisable to select an inductor with a saturation current ISAT higher than the possible peak current flowing through the inductor. The inductor's current rating IRMS should be higher than the average input current. The inductor peak current varies as a function of the load, the input and output voltages, and can be estimated by using Equation 7.

Equation 7. TPS61235P TPS61236P EQ_IL_Peak.gif

Where:

D is the duty cycle, and can be calculated by using Equation 5.

When estimating inductor peak current and average input current, the minimum input voltage, maximum output current, and minimum switching frequency in the application should be used for the worst case calculation. In this example, the minimum VIN is 3.0-V, maximum IOUT is 3-A, and minimum fsw is 750-kHz, so the inductor peak current result is 6.9-A, and the average input current is 5.9-A with an 85% efficiency estimation.

Selecting an inductor with insufficient saturation current can lead to excessive peak current in the converter. This could eventually harm the device and reduce reliability. To leave enough margin, it is recommended to choose saturation current 20% to 30% higher than IL_PEAK.

The following inductors are recommended to be used in designs if the current rating allows.

Table 3. List of Inductors

INDUCTANCE [µH] ISAT [A] IRMS [A] DC RESISTANCE [mΩ] PART NUMBER MANUFACTURER(1)
1 28 21.8 4.55 XAL7030-102ME Coilcraft
1 14.1 13 7.1 SPM6530T-1R0M120 TDK
1 19 11 9 FDSD0630-H-1R0M TOKO
1 11 6 23 SPM5020T-1R0M TDK

9.2.1.2.3.2 Output Capacitor Selection

For the output capacitor, it is recommended to use small X5R or X7R ceramic capacitors placed as close as possible to the VOUT and PGND pins of the IC. If, for any reason, the application requires the use of large capacitors which cannot be placed close to the IC, using a smaller ceramic capacitor of 1-µF or 0.1-µF in parallel to the large one is highly recommended. This small capacitor should be placed as close as possible to the VOUT and PGND pins of the IC.

The TPS6123x requires at least 20-µF effective capacitance at output for stability consideration. Care must be taken when evaluating a capacitor’s derating under bias. The bias can significantly reduce the effective capacitance. Ceramic capacitors can have losses of as much as 50% of their capacitance at rated voltage. Therefore, leave margin on the voltage rating to ensure adequate effective capacitance. In this example, three 22-µF capacitors of 10-V rating are used.

The ESR impact on the output ripple must be considered as well if tantalum or electrolytic capacitors are used. Assuming there is enough capacitance such that the ripple due to the capacitance can be ignored, the ESR needed to limit the VRipple is:

Equation 8. TPS61235P TPS61236P EQ_ESR.gif

9.2.1.2.3.3 Input Capacitor Selection

Multilayer X5R or X7R ceramic capacitors are an excellent choice for input decoupling of the step-up converter as they have extremely low ESR and are available in small footprints. Input capacitors should be located as close as possible to the device. The required minimum effective capacitance at input for the TPS6123x is 4.7-µF. Considering the capacitor’s derating under bias, a 10-µF input capacitor is recommended, and a 22-μF input capacitor should be sufficient for most applications. There is no limitation to use larger capacitors. It is recommended to put the input capacitor close to the VIN and PGND pins of the IC. If, for any reason, the input capacitor cannot be placed close to the IC, putting a small ceramic capacitor of 1-µF or 0.1-µF close to the IC's VIN pin and ground pin is recommended.

Take care when a ceramic capacitor is used at the input and the power is being supplied through long wires, such as from a wall adapter. A load step at the output may cause ringing at the VIN pin due to the inductance of the long wires. This ringing can couple to the output and be mistaken as loop instability or could even damage the part. Additional bulk capacitance (electrolytic or tantalum) should in this circumstance be placed between CIN and the power source to reduce ringing.

9.2.1.2.4 Loop Stability, Feed Forward Capacitor

One approach of stability evaluation is to look from a steady-state perspective at the following signals:

  • Switching node, SW
  • Inductor current, IL
  • Output ripple, VRipple(OUT)

When the switching waveform shows large duty cycle jitter or the output voltage or inductor current shows oscillations, the regulation loop may be unstable. This is often a result of board layout and/or L-C combination.

Load transient response is another approach to check loop stability. During the load transient recovery time, VOUT can be monitored for settling time, overshoot, or ringing that helps judge the converter’s stability. Without any ringing, the loop has usually more than 45° of phase margin.

To improve output voltage undershoot and overshoot performance during heavy load transient such as a 2-A load step transient, a feed forward capacitor Cff in parallel with R1 is recommended, as shown in Figure 17. The feed forward capacitor increases the loop bandwidth by adding a zero, so to achieve smaller output voltage undershoot, as shown in Figure 25. A 10-pF capacitor is suitable for most applications of the TPS6123x. See Application Note SLVA289 for more application notes of feed forward capacitor.

TPS61235P TPS61236P TypApp_3.0A_Cff.gif Figure 17. TPS61236P with Cff

9.2.1.2.5 INACT Pin Pull-up Resistor

The INACT pin can be used to report boost converter loading status to the MCU. It is an open drain output and should be connected with a pull up resistor. Normally a 1-MΩ resistor is recommended for the pull up resistor.

9.2.1.3 TPS61236P 5-V Output Application Curves

TPS61235P TPS61236P Wave1_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, IOUT = 3.1 A
Figure 18. Switching Waveforms in PWM Mode
TPS61235P TPS61236P Wave3_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, IOUT = 0 mA
Figure 20. Switching Waveforms in PFM Mode
TPS61235P TPS61236P Wave7_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, RL = 2.5 Ω
Figure 22. Shutdown Waveforms
TPS61235P TPS61236P Wave9_slvsck4.gif
VIN = 2.8 V to 3.3 V, VOUT = 5 V, IOUT = 2 A
Figure 24. Line Transient Response
TPS61235P TPS61236P Wave11_slvsck4.gif
VIN = 2.8 V to 3.3 V, VOUT = 5 V, IOUT = 2 A, Cff = 10 pF
Figure 26. Line Transient Response with Cff
TPS61235P TPS61236P Wave12_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, CC = 3.0 A, IOUT from 0 mA to 3 A
Figure 28. Load Sweep
TPS61235P TPS61236P D014_SLVSCK4.gif
RCC = 41.2 kΩ (CC current set to 3 A), VIN = 3.6 V
Figure 30. CC Pin Voltage vs Output Current with Different Ambient Temperatures
TPS61235P TPS61236P D016_SLVSCK4.gif
RCC = 61.9 kΩ (CC current set to 2 A), VIN = 3.6 V
Figure 32. CC Pin Voltage vs Output Current with Different Ambient Temperatures
TPS61235P TPS61236P Wave2_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, IOUT = 100 mA
Figure 19. Switching Waveforms in PFM Mode
TPS61235P TPS61236P Wave5_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, RL = 2.5 Ω
Figure 21. Startup
TPS61235P TPS61236P Wave8_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, IOUT = 500 mA to 2 A
Figure 23. Load Transient Response
TPS61235P TPS61236P Wave10_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, IOUT = 500 mA to 2 A, Cff = 10 pF
Figure 25. Load Transient Response with Cff
TPS61235P TPS61236P Wave14_slvsck4.gif
VIN = 3.6 V, VOUT = 5.1 V, RCC = 41.2 kΩ, RL = 2.5 Ω to 1.5 Ω
Figure 27. Constant Current Response
TPS61235P TPS61236P D013_SLVSCK4.gif
RCC = 41.2 kΩ (CC current set to 3 A), TA = 25°C
Figure 29. CC Pin Voltage vs Output Current with Different Inputs
TPS61235P TPS61236P D015_SLVSCK4.gif
RCC = 61.9 kΩ (CC current set to 2 A), TA = 25°C
Figure 31. CC Pin Voltage vs Output Current with Different Inputs

9.2.2 TPS61236P 2.3-V to 5-V Input, 5-V 2-A Output Converter

In this application, the TPS6123x is required to be used as a standard boost converter to output 5-V voltage and maximum 2-A current. The Constant Current function should be disabled, and the INACT function is not needed either.

TPS61235P TPS61236P TypApp_justBst.gif Figure 33. TPS61236P 5-V 2-A Output Typical Application

9.2.2.1 Design Requirements

The design parameters for the TPS61236P 5-V output current design are listed in Table 4.

Table 4. TPS61236P 5-V Output Design Parameters

DESIGN PARAMETERS EXAMPLE VALUES
Input voltage range 2.3 V to 4.4 V
Output voltage 5 V
Output current rating 2 A
Operating frequency 1 MHz

9.2.2.2 Detailed Design Procedure

Refer to the Detailed Design Procedure section for the detailed design steps.

Because the CC function and the INACT function are not needed, the user can simply connect the two pins to ground to disable the functions as shown in Figure 33.

9.2.2.3 TPS61236P 5-V Output Application Curves

TPS61235P TPS61236P D004_SLVSCK4.gif
VOUT = 5.1 V (TPS61235P), CC pin connected to GND
Figure 34. Maximum Load Capability after Startup
TPS61235P TPS61236P D006_SLVSCK4.gif
VOUT = 5.1 V (TPS61235P), CC pin connected to GND
Figure 36. Load Regulation
TPS61235P TPS61236P Wave13_slvsck4.gif
VIN = 3.6 V, VOUT = 5 V, IOUT from 0 mA to 4 A
Figure 38. Load Sweep
TPS61235P TPS61236P D005_SLVSCK4.gif
VOUT = 4.5 V (TPS61236P), CC pin connected to GND
Figure 35. Load Regulation
TPS61235P TPS61236P D007_SLVSCK4.gif
VOUT = 5.5 V (TPS61236P), CC pin connected to GND
Figure 37. Load Regulation